Conventionally, NAND memory devices have been used as nonvolatile semiconductor memory devices. In a NAND memory device, the upper layer portion of the silicon substrate is partitioned into multiple portions having line configurations; and these portions having line configurations are used as active areas. Multiple memory cells are formed in each of the active areas; and a pair of selection gate electrodes is provided on two sides of the multiple memory cells respectively. A bit line and a source line are provided above the silicon substrate and are connected to the pair of selection gate electrodes on the two sides. At this time, at least the bit line is connected to the active area via a contact.
However, the short margin between mutually-adjacent contacts undesirably decreases as downscaling of the NAND memory device progresses. For example, in the case where the contact diameter enlarges excessively due to the fluctuation of the manufacturing processes, there is a risk that two of the contacts connected to mutually-adjacent active areas may undesirably short to each other. Therefore, technology has been proposed to arrange the contacts in a staggered configuration as viewed from above.
However, although the short margin between the contacts can be improved by arranging the contacts in the staggered configuration, the short margin between the contact and the active area is not improved. In other words, there is a risk of the contact connected to one active area being shorted to an active area disposed adjacently to the one active area in the case where the spacing between the active areas is reduced. Therefore, the product yield undesirably decreases when shrinking the NAND memory device.
Although the necessary short margin is reduced if the formation positions of the contacts are controlled with high precision, there is a limitation on increasing the precision of the lithography. Although it is conceivable to make the contacts finer to ensure the short margin, in the case where the contacts are made finer, the contact resistance increases, the cell current decreases, and the difficulty when making the contact holes increases. Therefore, there is a possibility that open defects may increase.